(1) Field of the Invention
The instant invention relates to submersible vessels and more particularly to an actuator mechanism for operating a torpedo tube shutter door.
(2) Description of the Prior Art
Referring to the drawing FIGS. 1 and 2, the prior art actuator mechanism for operating a hinged torpedo tube shutter door 10 is illustrated and it is generally indicated at 12. It is noted that FIG. 1 shows the mechanism 12 in the closed position and that FIG. 2 shows the mechanism 12 in the open position. The torpedo tube shutter door 10 is a long rectangular shaped fairing plate which streamlines the outer hull 14 of a submarine when the submarine's torpedo tube outer door is closed. The shutter door 10 is necessary to prevent flow turbulence in the flow field of the submarine as it propels itself through the water. Prior to firing a torpedo, the shutter door 10 is opened to provide a clear path for the torpedo to be ejected from within the ship. It is noted that the shutter door 10 is not a pressure containing door as this function is accomplished by a much stronger pressure sealed torpedo tube muzzle door. In addition, there is no pressure seal between the shutter door 10 and the outer hull 14. Therefore, there are no forces on the shutter door 10 which are attributable to sea pressure. However, the shutter door 10 is subjected to hydrodynamic flow over its surface. Since the firing line 16 of an ejected torpedo typically intersects the outer hull 14 at an angle anywhere from 12.degree. to 14.5.degree., the shutter door 10 may be quite long, and therefore the hydrodynamic forces exerted thereon can be quite significant. For example, if the flow velocities across a shutter door produce a 10 psi pressure differential, then a 30 sq. ft. shutter door (4320 sq. in.) would have to overcome a 43,200 pound force plus the shutter's own weight and any system binding forces before it could be operated. While the shutter door is not a pressure containing member, it is designed to be relatively stiff via the use of stiffening members to prevent shutter vibration and deflection and therefore a shutter door may weigh between 1500 and 1800 pounds.
In the existing prior art assembly as illustrated in FIGS. 1 and 2, the power to operate the mechanism 12 comes from a hydraulic cylinder 17 through a power transmission link 18 which provides force to overcome the system moments and weights, forces due to misalignment and binding parts, and the hydrodynamic loads on the shutter door 10 due to the ship's forward motion through the water. Although the system moments and weights can be accurately calculated prior to the actual manufacture of the hardware, the forces due to misalignment and binding of the parts are difficult to calculate due to the varying deflection of parts with varying ship's depths and manufacturing tolerances. The quantification of hydrodynamic loads is equally as difficult to calculate because the hydrodynamic flow, pressure points, and flow vortices vary with different ship's speeds and maneuvers, and varying positions of the shutter door 10 between the fully open and fully closed positions. Unfortunately, the only accurate method to determine these forces is to conduct a full scale ship's test. However, not even a ship's test is 100% accurate due to the variations in construction between like ships in a class. Even if these variation were ignored, such a test would be extremely expensive and could only be conducted after it was too late to incorporate the results into the ship's basic design.
The prior art shutter mechanism 12 is pivotably connected between the inner hull 20 and the shutter door 10 via a series of interconnected links which draw the shutter door inwardly when force is applied through the hydraulic cylinder link 18. In operation of the mechanism 12, the hydraulic cylinder link 18 exerts force to the right as viewed in the drawings figures. The hydraulic cylinder link 18 is pivotably connected to links 22 and 24, and link 22 is pivotally connected to the inner hull 20 at pivot point 26. Movement of hydraulic cylinder link 18 to the right pivots link 22 counterclockwise about point 26 and forces link 24 to the right. Link 24 is pivotably connected to a torque arm 28. The torque arm 28 and a transfer link 30 are keyed to a common shaft 32 which rotates about pivot point 34. Therefore, when link 24 moves to the right, it pivots both links 28 and 30 counterclockwise about pivot point 34. Link 30 is pivotably connected to a connector link 36 at pivot point 38, and link 36 is in turn pivotably connected to the shutter door 10 at pivot point 40. As link 30 rotates in a counterclockwise direction, it moves the end of the link, i.e. pivot point 38, inwardly away from the outer hull 14. As link 30 further rotates away from the outer hull 14, it draws link 36 and the shutter door 10 inwardly. The shutter door 10 is pivotably connected to the outer hull 14 at pivot point 42, and is thus free to move inward as it rotates about pivot point 42. It is necessary to utilize this complex linkage system to prevent the shutter door 10 from inadvertently opening inward due to wave slap. It is pointed out that in the fully closed position, pivot point 38 is located slightly to the left of a straight line drawn between pivot point 34 and pivot point 40. This arrangement permits force from wave slap to be transmitted via the linkage to hydraulic cylinder link 18 which has a positive stop, thus preventing it from moving in the direction of the force. Therefore, it can be seen that the shutter door 10 will not open due to wave slap.
Because of the difficulty in accurately calculating all the potential forces which are exerted on the shutter door, it has been found that the power generated by the prior art mechanism is often insufficient to operate the shutter door under all operating conditions. This flaw in the prior art mechanism can cause significant problems because the inability to operate the shutter door prevents a submarine from being able to fire its torpedoes.
Several solutions to the problem have previously been suggested. The most obvious method to eliminate the torque problems of operating a shutter door would be to replace the hinged shutter doors with rotating shutters. However, this solution is plagued by several problems which relate to the large physical size of rotating shutters. The larger size of a rotating shutter would require extensive modifications of the forward portions of the ship in order to fit the rotary shutter in place. Such extensive ship modifications, whether in a new ship or an existing ship, are cost prohibitive. In addition, there are also problems associated with misalignment of the shutter and deflection of parts.
Another possible solution is to utilize a larger and more powerful hydraulic cylinder 17 to operate link 18. If a larger, more powerful hydraulic cylinder 17 was backfit into an existing design, the larger cylinder 17 would most likely have a larger shaft size. The added power and increased shaft size would require that all the components interconnected with the hydraulic cylinder 17 be strengthened in a like manner. Such a design would also most likely require new support bearings, a new hull stuffing box, and replacement of all the interlock mechanisms, pins, and hinges which transmit or have force applied to them. As a result such a design would be very costly to implement. If the larger hydraulic cylinder 17 were integrated into a new ship construction, it is quite likely that the larger stronger components would not fit in the same space available and thus the forward portions of the ship would also have to be redesigned.
Still another possible solution is to lengthen the travel of the hydraulic power cylinder 17 to facilitate a better mechanical advantage to the shutter door linkage. This type of design is also plagued by a multitude of problems. If the longer hydraulic cylinder were backfit into an existing ship, the increased travel distance would require the shaft bearing supports to be spaced further apart. In addition, the interlock system, support brackets, links, and hinge pivot points would have to be relocated to be compatible with the modified cylinder travel. If it were possible to fit these modified parts into the existing space available, then cost, shock, and timing requirements would have to be addressed. This design would also likely require the use of a larger hydraulic cylinder to withstand shock loads. In addition, the increased travel distance would also cause a longer actuation time due to increased travel length. This could be a critical factor in situations where it is desired to quickly fire weapons in an emergency.
Yet another potential solution for correcting the problem in an existing ship would be to redesign some components to minimize assembly binding and to control pressure differentials caused by hydrodynamic flow. The problem with this solution is that it is impossible to ensure complete system alignment at all depths of operation and to ensure maintenance of system alignment as components wear. In addition, once a ship system is designed, it is difficult to significantly alter the forces resulting from hydrodynamic flow.
In spite of the previously noted alternatives, it is still possible that the shutter doors would not operate under all conditions. Such a failure could result because it is impossible to determine with 100% accuracy all the forces which will be exerted on an operational shutter door.